1. Field of the Invention
The present invention relates to a magnetoresistive device substructure including magnetoresistive elements, a magnetoresistive device including a magnetoresistive element, and a micro device including a first patterned thin film and a second patterned thin film that covers the first thin film, and to methods of manufacturing such a magnetoresistive device substructure, a magnetoresistive device and a micro device.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a recording head having an induction-type electromagnetic transducer for writing and a reproducing head having a magnetoresistive element for reading.
Reproducing heads that exhibit high sensitivity and produce high outputs have been required. In response to such demands, attention has been focused on tunnel magnetoresistive elements (that may be hereinafter called TMR elements) that detect a magnetic field through the use of the tunnel magnetoresistive effect.
As shown in FIG. 21, the TMR element has a structure in which a lower magnetic layer 102, a tunnel barrier layer 103 and an upper magnetic layer 104 are stacked on a substrate 101. Each of the lower magnetic layer 102 and the upper magnetic layer 104 includes a ferromagnetic substance. In general, the magnetic layer closer to the substrate is called the lower magnetic layer and the magnetic layer farther from the substrate is called the upper magnetic layer. Therefore, the terms xe2x80x98upperxe2x80x99 and xe2x80x98lowerxe2x80x99 of the upper and lower magnetic layers do not always correspond to the position in the arrangement of an actual TMR element.
The tunnel barrier layer is a layer made of a thin nonmagnetic insulating film through which electrons are capable of passing while maintaining spins thereof by means of the tunnel effect, that is, through which a tunnel current is allowed to pass. The tunnel magnetoresistive effect is a phenomenon that, when a current is fed to a pair of magnetic layers sandwiching the tunnel barrier layer, a tunnel current passing through the tunnel barrier layer changes, depending on the relative angle between magnetizations of the two magnetic layers. If the relative angle between magnetizations of the magnetic layers is small, the tunneling rate is high. As a result, the resistance to the current passing across the magnetic layers is reduced. If the relative angle between magnetizations of the magnetic layers is large, the tunneling rate is low. The resistance to the current passing across the magnetic layers is therefore increased.
With regard to the structure of a thin-film magnetic head incorporating a TMR element, if the tunnel barrier layer made up of a thin insulating layer is exposed from the medium facing surface that faces toward a recording medium, a short circuit may occur during or after lapping of the medium facing surface. Such a structure is therefore not preferred.
To cope with such a problem, a thin-film magnetic head is disclosed in U.S. patent application Ser. No. 09/517,580. This head has a structure in which a TMR element retreats from the medium facing surface. FIG. 22 and FIG. 23 illustrate a front-flux-probe-type head as an example of the head having such a structure. FIG. 22 is a cross section of the main part of the head. FIG. 23 is a top view thereof This head comprises a pinning layer 105, a pinned layer 106, a tunnel barrier layer 107 and a free layer 108 that are stacked one by one. These layers make up the TMR element. The TMR element is located at a distance from the medium facing surface.
The head further comprises a front flux probe (FFP) layer 109 formed on the free layer 108. The FFP layer 109 is T-shaped and includes two portions one of which extends from the medium facing surface to a portion above the free layer 108, and the other of which is located in the portion above the free layer 108 and extends from side to side along the direction parallel to the medium facing surface. The FFP layer 109 is a soft magnetic layer that directly touches the TMR element. As shown in FIG. 22 and FIG. 23, the FFP layer 109 may be formed by adding a soft magnetic layer different from the TMR element in size. Alternatively, the FFP layer 109 may be made of a part of the free layer 108 of the TMR films.
The portion 109a of the FFP layer 109 that extends to the medium facing surface has the function of introducing a signal magnetic flux from the medium facing surface to the TMR element. The length of the portion 109a is called the front flux probe length (FFP length of FIG. 23).
The head further comprises a pair of hard magnet layers 110 located on the portion of the FFP layer 109 extending from side to side.
Another function of the FFP layer 109 is to effectively give the free layer of the TMR element a bias magnetic field in the horizontal direction obtained from the bias field applying layers such as the hard magnet layers and antiferromagnetic substances. In the case of the TMR element, as in the cases of an anisotropic magnetoresistive (AMR) element and a giant magnetoresistive (GMR) element, a short circuit occurs if the bias field applying layer touches an end of the element. As a result, no rate of change in resistance is detected. If the bias field applying layer directly touches a top portion or a bottom portion of the TMR element, no short circuit occurs. However, the problem is that, if the direction of magnetization of the pinned layer and the direction of magnetization of the free layer are antiparallel with respect to each other, a greater current flows through a portion of the tunnel barrier layer in which the bias field applying layer is located. As a result, the rate of change in resistance is reduced.
To solve the above-described problem, a technique is disclosed in U.S. patent application Ser. No. 09/517,455. According to this technique, a soft magnetic layer greater than a TMR element in width along the track width is formed. The soft magnetic layer has a portion located outside the TMR element. A bias field applying layer is located in this portion. This soft magnetic layer has the function of effectively inducing a bias field from the bias field applying layer to the free layer of the TMR element. The FFP layer 109 of FIG. 22 and FIG. 23 corresponds to this soft magnetic layer.
As described above, the FFP layer 109 having the functions of introducing a signal flux and inducing a bias field is T-shaped.
If the conventional photolithography technique is employed, the problem is that corners of a pattern reduced in size are rounded. The above-described front-flux-probe-type head has a reproducing track width which is defined by the width of the front flux probe layer measured in the medium facing surface. Therefore, it should be avoided that corners of the front flux probe layer formed through the photolithography technique are rounded, since such rounded corners cause variations in track width. To avoid this problem, an electron beam exposure technique may be employed. In this case, however, the throughput is reduced while manufacturing costs increase since the apparatus required for electron beam exposure is expensive.
To reduce roundness of corners of the pattern, it is possible to provide the front flux probe layer having the shape of a rectangle greater than the TMR element, in place of the T-shaped front flux probe layer. However, this solution is not preferred since it is impossible that the track width is made smaller than the width of the TMR element.
To precisely control the dimensions and shape of the T-shaped soft magnetic layer having the functions of introducing a signal flux and inducing a bias field, it is possible to make the T-shaped soft magnetic layer in two steps by dividing it into two rectangular layers. Reference is now made to FIG. 24A to FIG. 33A and FIG. 24B to FIG. 33B to describe a method of manufacturing a magnetoresistive device including a soft magnetic layer formed through this method.
FIG. 24A to FIG. 33A and FIG. 24B to FIG. 33B illustrate steps of the method of manufacturing the magnetoresistive device including the soft magnetic layer and a TMR element. FIG. 24A to FIG. 33A are cross sections thereof FIG. 24B to FIG. 33B illustrate integrated surfaces.
In this method, as shown in FIG. 24A and FIG. 24B, a pinning layer 112, a pinned layer 113, a tunnel barrier layer 114 and a free layer 115 are stacked on a substrate 111 one by one.
Next, as shown in FIG. 25A and FIG. 25B, a resist mask 116 used for patterning the TMR element is formed by photolithography on the free layer 115.
Next, as shown in FIG. 26A and FIG. 26B, the pinning layer 112, the pinned layer 113, the tunnel barrier layer 114 and the free layer 115 are selectively etched through ion milling, for example, using the resist mask 116. The TMR element 120 made up of the pinning layer 112, the pinned layer 113, the tunnel barrier layer 114 and the free layer 115 that are patterned is thus formed.
Next, as shown in FIG. 27A and FIG. 27B, an insulating layer 117 is formed around the TMR element 120. The resist mask 116 is then removed.
Next, as shown in FIG. 28A and FIG. 28B, a bias field inducing layer 118 made of a soft magnetic material is formed on the TMR element 120 and the insulating layer 117.
Next, as shown in FIG. 29A and FIG. 29B, a resist mask 119 used for patterning the bias field inducing layer 118 is formed by photolithography on the layer 118. The plane geometry of the resist mask 119 is a rectangle extending from the portion above the TMR element 120 to both sides in the direction parallel to the medium facing surface.
Next, as shown in FIG. 30A and FIG. 30B, the field inducing layer 118 is selectively etched through ion milling, for example, using the resist mask 119. The field inducing layer 118 is thereby patterned into a rectangular shape. The resist mask 119 is then removed.
Next, as shown in FIG. 31A and FIG. 31B, a front flux probe (FFP) layer 121 made of a soft magnetic material is formed on the insulating layer 117 and the field inducing layer 118.
Next, as shown in FIG. 32A and FIG. 32B, a resist mask 122 used for patterning the FFP layer 121 is formed by photolithography on the layer 121. The plane geometry of the resist mask 122 is a rectangle extending from the portion above the TMR element 120 toward the medium facing surface.
Next, as shown in FIG. 33A and FIG. 33B, the FFP layer 121 is selectively etched through ion milling, for example, using the resist mask 122. The FFP layer 121 is thereby patterned into a rectangular shape. The resist mask 122 is then removed.
The T-shaped soft magnetic layer having the functions of introducing a signal flux and inducing a bias field is thus made up of the field inducing layer 118 and the FFP layer 121.
According to the above-described method, however, the resist mask 119 used for patterning the field inducing layer 118 is greater in area than the TMR element 120. As a result, when the resist mask 119 is formed, the TMR element 120 is hidden behind the resist mask 119, and alignment of the resist mask 119 and the TMR element 120 is made impossible. The positions of the TMR element 120 and the field inducing layer 118 with respect to each other are thereby shifted, which will cause variations in output.
In general, a flying-type thin-film magnetic head used for a magnetic disk drive is made up of a slider having a thin-film magnetic head element formed on its trailing edge. The slider has rails formed on the medium facing surface that faces toward a recording medium, and flies at a very low altitude from the surface of the recording medium by means of the air flow generated by rotations of the medium. The slider is formed through the following steps. A substructure utilized is made up of a plurality of rows of sections to be sliders (hereinafter called slider sections) formed on a wafer. Each of the slider sections includes a thin-film magnetic head element. This substructure is cut in one direction to form blocks called bars each of which is made up of a row of slider sections. Each of the bars is lapped to form the medium facing surface. Rails are then formed in the medium facing surface. Next, the bar is divided into individual sliders.
Outputs of a front-flux-probe-type head greatly varies, depending on the front flux probe length. It is therefore very important to control the front flux probe length. The front flux probe length is controlled by an amount of lapping of the medium facing surface of the above-mentioned bar.
However, an overcoat layer made of alumina (Al2O3), for example, and having a thickness of tens of micrometers is formed on the integrated surface, after the medium facing surface of the bar is lapped, that is, after the front flux probe length is determined. It is therefore impossible to directly observe the FFP layer through the use of a scanning electron microscope, for example. A currently possible method is to cut out a part of the head by a focused ion beam and to observe its cross section through the use of a transmission electron microscope, for example. However, this method is breakdown measurement and it is impossible to apply the measurement result to processing and so on of the sample itself, which is not preferred. Furthermore, this method is not practical since it takes a long time to perform cutting of the head by a focused ion beam and observing through the use of a transmission electron microscope. It is therefore difficult to control the front flux probe length of the head having the FFP layer. Variations in outputs thereby result.
It is a first object of the invention to provide a magnetoresistive device substructure or a magnetoresistive device, or a method of manufacturing such a magnetoresistive device substructure or a magnetoresistive device. With regard to the magnetoresistive device including the magnetoresistive element and a soft magnetic layer having at least one of the function of introducing a signal field to the magnetoresistive element and the function of inducing a bias field thereto, the substructure or the device, or the method of the invention allows precise control of the arrangement of the magnetoresistive element and the soft magnetic layer with respect to each other and the dimensions of the soft magnetic layer, and reduces variations in output.
It is a second object of the invention to provide a micro device or a method of manufacturing such a micro device, the micro device including a first patterned thin film and a second patterned thin film that covers the first thin film. The micro device or the method of the invention allows precise control of the arrangement of the first and second thin films with respect to each other and the dimensions of the second thin film.
A magnetoresistive device substructure of the invention is used for manufacturing a magnetoresistive device incorporating: a magnetoresistive element; and a soft magnetic layer covering the magnetoresistive element and having at least one of functions of introducing a signal magnetic flux to the magnetoresistive element and inducing a bias magnetic field thereto. The substructure comprises: the magnetoresistive element; the soft magnetic layer; and an indicator having a shape similar to the magnetoresistive element and located in a specific position with respect to the magnetoresistive element.
A magnetoresistive device of the invention comprises: a magnetoresistive element; a soft magnetic layer covering the magnetoresistive element and having at least one of functions of introducing a signal magnetic flux to the magnetoresistive element and inducing a bias magnetic field thereto; and an indicator having a shape similar to the magnetoresistive element and located in a specific position with respect to the magnetoresistive element.
According to the magnetoresistive device substructure or the magnetoresistive device of the invention, it is possible to control the arrangement of the magnetoresistive element and the soft magnetic layer with respect to each other and to control the dimensions of the soft magnetic layer through the use of the indicator.
According to the magnetoresistive device substructure or the magnetoresistive device of the invention, the indicator may be a dummy element having a configuration similar to that of the magnetoresistive element and being incapable of functioning as a magnetoresistive element.
The magnetoresistive device substructure or the magnetoresistive device of the invention may further comprise a dummy layer located in a specific position with respect to the soft magnetic layer and located off the indicator.
The magnetoresistive device substructure or the magnetoresistive device of the invention may further comprise an overcoat layer covering the soft magnetic layer and having an opening located in a portion corresponding to the indicator.
According to the magnetoresistive device substructure of the invention, the indicator may be located in a position at which the substructure is divided to fabricate the magnetoresistive device.
A method of the invention is provided for manufacturing a magnetoresistive device substructure used for manufacturing a magnetoresistive device incorporating: a magnetoresistive element; and a soft magnetic layer covering the magnetoresistive element and having at least one of functions of introducing a signal magnetic flux to the magnetoresistive element and inducing a bias magnetic field thereto. The method comprises the steps of: forming the magnetoresistive element and an indicator having a shape similar to the magnetoresistive element and located in a specific position with respect to the magnetoresistive element; and forming the soft magnetic layer in a specific position referring to the position of the indicator.
A method of the invention is provided for manufacturing a magnetoresistive device incorporating: a magnetoresistive element; and a soft magnetic layer covering the magnetoresistive element and having at least one of functions of introducing a signal magnetic flux to the magnetoresistive element and inducing a bias magnetic field thereto. The method comprises the steps of: forming the magnetoresistive element and an indicator having a shape similar to the magnetoresistive element and located in a specific position with respect to the magnetoresistive element; and forming the soft magnetic layer in a specific position referring to the position of the indicator.
According to the method of manufacturing the magnetoresistive device substructure or the method of manufacturing the magnetoresistive device of the invention, it is possible to control the arrangement of the magnetoresistive element and the soft magnetic layer with respect to each other and to control the dimensions of the soft magnetic layer through the use of the indicator.
According to the method of manufacturing the magnetoresistive device substructure or the method of manufacturing the magnetoresistive device of the invention, the indicator may be a dummy element having a configuration similar to that of the magnetoresistive element and being incapable of functioning as a magnetoresistive element.
According to the method of manufacturing the magnetoresistive device substructure or the method of manufacturing the magnetoresistive device of the invention, in the step of forming the soft magnetic layer, a dummy layer may be formed at the same time as the soft magnetic layer, the dummy layer being located in a specific position with respect to the soft magnetic layer and located off the indicator.
The method of manufacturing the magnetoresistive device substructure or the method of manufacturing the magnetoresistive device of the invention may further comprise the step of forming an overcoat layer covering the soft magnetic layer and having an opening located in a portion corresponding to the indicator.
The method of manufacturing the magnetoresistive device substructure or the method of manufacturing the magnetoresistive device of the invention may further comprise the steps of: forming an overcoat layer covering the soft magnetic layer and the indicator; and forming an opening of the overcoat layer by selectively etching a portion of the overcoat layer that corresponds to the indicator. In this case, either of the methods may further comprise the step of forming a film for stopping reactive ion etching on the indicator prior to the step of forming the overcoat layer, wherein the opening is formed through the reactive ion etching in the step of forming the opening.
According to the method of manufacturing the magnetoresistive device substructure or the method of manufacturing the magnetoresistive device of the invention, the indicator may be located in a position at which the substructure is divided to fabricate the magnetoresistive device.
A micro device of the invention includes a first patterned thin film and a second patterned thin film covering the first thin film. The device further comprises an indicator having a shape similar to the first thin film and located in a specific position with respect to the first thin film.
A method of the invention is provided for manufacturing a micro device including a first patterned thin film and a second patterned thin film covering the first thin film. The method comprises the steps of forming the first thin film and an indicator having a shape similar to the first thin film and located in a specific position with respect to the first thin film; and forming the second thin film in a specific position referring to the position of the indicator.
According to the micro device or the method of manufacturing the same of the invention, it is possible to control the arrangement of the first and second patterned thin films with respect to each other and to control the dimensions of the second thin film through the use of the indicator. In the present patent application the micro device means a small-size device fabricated through the use of thin-film forming techniques.
Other and further objects, features and advantages of the invention will appear more fully from the following description.